Some Fiat Electrical Basics: Part 1

[zachmac]

I have been reading, and writing about, and fixing Fiat Spider wiring now for about 10 years. I thought I knew a lot but just recently I think I came to some new understanding and I think it is worth sharing. This Part 1 will lay some foundation. Part 2 will address the implications of this foundation on replacement Lada ignition switch use and wiring. Part 3 will describe a better solution to a “problem” part 2 creates, and part 4 will review the typical Fiat Spider fuse power supply sources and loads.

NOTE: I take no responsibility for work you or someone else does on you car and the results. I have taken every precaution I can think of to get all this right but I cannot control the actions of others.

The first thing every Spider owner should do in my opinion is go to http://www.Mirafiori.com and read the electrical postings in the FAQ section. Lots of people have contributed good stuff there. Most important to my discussion are this link: https://www.mirafiori.com/faq/content/bwfix/bwfix.htm and this link: https://www.mirafiori.com/faq/content/s ... witch.html. Go read these first. No, really go read them then come back here. When you do read them be aware of two minor (but important) errors in the write ups:

1) In the “Brown” Wire Fix article the author says the Brown wire is the only 12V feed to the switch and that therefore all power to the car has to go through a single contact. This is NOT true. There is in fact the Brown wire 12V feed to post #30 AND a black wire 12V feed to post #30/1.

2) In the second post, Troubleshooting the Ignition Switch on the Fiat Spider, there is again a minor, but important to get right, error. In discussing the “Left Side” circuit the author correctly states that it is comprised of a Brown, Red and Bl/BK wire (Blue with black trace). But when stating the connections between them in various switch positions he incorrectly described the BL/BK wire as Black. Again, important since there is a black wire but it is on the other side, in the other switch circuit, and performs a very different function.

With this base understanding of the switch and its two circuits we can begin with new info. Thank you to that author of the Mirafiori posts for his contribution. We stand on the shoulders of giants.

Three types of Power:
All of the power for your car comes in one of three varieties, Unswitched, Switched (Continuous Need) and Switched (Situational Needs).

Note: technically the power to your starter and the hot alternator post are separate and you do need to understand those are direct, unfused, hot loads. Take great care when working in those areas; much arcing, sparking and damage can occur. Always disconnect the battery when working on the starter or alternator. Those connection points are where power to everything else is fed from.

Unswitched – these are items the battery provides power to without passing through the ignition switch. It does this by a black wire from the Starter main post / alternator hot post, through the firewall, to the “top” or input side of the fuse box. This same black wire is continued from the fuse box to terminal #30/1 on the ignition switch as a POWER INPUT. Loads powered from the unswitched fuses are for example the parking lights when the light switch is in the first position, the lighter, sometimes the radio, the horn, the clock, the courtesy light, or the radiator cooling fan. Loads that need to run or you may want to run when the car is off and the key is not in the ignition. Note that the exact list of these loads varied year to year so check your specific year’s owner’s manual or wiring diagrams. The loads are ALWAYS powered when the battery is connected regardless of ignition switch status, hence the name UNSWITCHED.

Switched (Continuous Need) – these are loads that the car needs power for to run and be safely monitored. Things like ignition, sensors, gauges, electric fuel pumps, FI relays and injectors if FI car, etc. In general they are loads that the driver doesn’t switch on and off via a second switch. They need power any time you are driving. These loads receive power from the fuses that are fed by the Pink wire from post #15 / 54 on the ignition switch. The Pink wire gets its power from the Black wire feeding post #30/1 when the ignition switch is ON or in the START position. On a stock SIPEA switch and a Lada replacement switch these two wires are not connected and these loads are not powered when in OFF or locked / key removed.

Switched (Situational Needs) – these are loads that only require power in certain situations. Wipers when it rains, headlights when it is dark, heater blower motor when you are cold. What all of these have in common is that they have power routed to a SECOND SWITCH that controls them, fed from fuses that the ignition switch powers when in RUN or START. BUT in this case that power is only used when that second switch is also in a certain position. The power to these fuses is coming into the ignition switch from the BROWN #30 post wire and passing to the BL/BK (blue with black trace) post #INT wire. The only difference between ON and START is the latter spring loaded position also feeds BROWN wire power to the RED #50 post wire to power the starter solenoid and crank the engine. The stock SIPEA switch only power these loads when in the ON or START key positions. It does not power them in OFF or key removed. The replacement Lada switch also powers these when in RUN or START BUT, and THIS IS IMPORTANT, also powers these when the key is in locked / key removed position. It BTW does not power them when in OFF with the key inserted.

This then lays the groundwork for Part 2, how should you really wire that new Lada ignition switch?

[RRoller123]

This series is extremely helpful. Thank you very much for your effort and dedication in in this work, and for posting it for all to share.